Physics question

How can I calculate the intensity of radiation of the Sun at Earth(at the same distance as the Earth is at). The intenisity of radiation at the Sun is about 64MW/m2. I mean the radiation spreads around so how can I know which portion comes to the Earth?

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well saying that the radiation from the sun all travels at the same speed
, this radiation will cover a spherical shape of area.(just like blowing a balloon)

now the distance of the earth to the sun is about
this means you need to find the surface area of a sphere with a radius of , then you need to find the area of intersection between the sphere and the earth(assume to be in the middle of the earth)

surface area of the sphere:
where is the radius of the earth and has the value of

hence the area of intersection is:

where is the radius of the earth and has the value of . The area of intersection is can be assumed as a circle since the distance of the earth from the sun is very much larger tahn the radius of the earth.